Joins on same table

[Chris]

I'm having two general problems trying to do a JOIN. I have a table with
three fields {Code, Date, Amount}. Code+Date is a unique key. I'm trying
to get a rowset with 1) one row for each unique Code+Date pair, 2) and
with each row containing, {Code, Amount for Date-A and Amount for
Date-B}. Basically, I want to create two temp tables with the Amounts for
a specified Date and then Join them.

The problems are
1) I'm trying to do this in SQL-Server 7 with a single stantment, and
2) If a Code+Date pair doesn't have any Amounts, I'd still like a row
returned with NULLs.

Anybody have any wisdom on this??
Thanks

[Chris]

Re: Joins on same table .. solution with Temps

The following gets me what I want, using Temp tables. I'm just trying to
figure out how to combine the Selects into a single statment.

Thanks

--------------------------------------------------

--temp with each Code
Drop Table #T0;
Select Code
Into #T0
From tblSearch
Order by Code;

--temp with amounts for 1st date
Drop Table #T1;
Select Code, Date, Amount
Into #T1
From tblSearch
Where Date = 20031102
Order by Code, Date;

-- amounts for 2nd date
Drop Table #T2;
Select Code, Date, Amount
Into #T2
From tblSearch
Where Date = 20031103
Order by Code, Date;

--put everything together
Select Distinct #T0.Code, #T1.Date, #T1.Amount 'd1', #T2.Date, #T2.Amount
'd2' from #T0
Left Outer Join #T1
On #T0.Code = #T1.Code
Left Outer Join #T2
On #T0.Code = #T2.Code
Order By #T0.Code

[Erland Sommarskog]

Re: Joins on same table

[posted and mailed, please reply in news]

Chris (chris@hicom.ne t) writes:[color=blue]
> I'm having two general problems trying to do a JOIN. I have a table
> with three fields {Code, Date, Amount}. Code+Date is a unique key.
> I'm trying to get a rowset with 1) one row for each unique Code+Date
> pair, 2) and with each row containing, {Code, Amount for Date-A and
> Amount for Date-B}. Basically, I want to create two temp tables with
> the Amounts for a specified Date and then Join them.
>
> The problems are
> 1) I'm trying to do this in SQL-Server 7 with a single stantment, and
> 2) If a Code+Date pair doesn't have any Amounts, I'd still like a row
> returned with NULLs.[/color]

Just rewriting the temp-table thing you had with derived tables
gives:

SELECT DISTINCT #T0.Code, #T1.Date, #T1.Amount 'd1',
#T2.Date, #T2.Amount 'd2'
FROM tblSearch #T0
LEFT JOIN (SELECT Code, Date, Amount
FROM tblSearch
WHERE Date = '20031102') AS #T1
ON #T0.Code = #T1.Code
LEFT JOIN (SELECT Code, Date, Amount
FROM tblSearch
WHERE Date = '20031103') AS #T2
ON #T0.Code = #T2.Code
ORDER BY #T0.Code

But if I understand this correctly, it seems that you could get away with:

SELECT Code = coalesce(a.Code , b.Code), a.Date, d1 = a.Amount,
b.Date, d2 = b.Amount
FROM tblSearch a
FULL JOIN tblSearch b ON a.Code = b.Code
AND a.Date = b.Date
AND a.Date = '20031102'
AND b.Date = '20031103'


All this works on SQL7.

--
Erland Sommarskog, SQL Server MVP, sommar@algonet. se

Books Online for SQL Server SP3 at

http://www.microsoft.com/sql/techinfo/productdoc/2000/books.asp

[louis nguyen]

Re: Joins on same table .. solution with Temps

Hi Chris,

You can replace temp tables with derived tables. Alternatively, as
the temp tables are selecting from the same table tblSearch, you can
also re-write the query using CASE. Note I'm using a mssqlserver
non-standard syntax. I just find it easier to read.

"Date=CASE when Date = 20031102 then Date else null end"
instead of
"CASE when Date = 20031102 then Date else null end as Date"

SELECT
Distinct
Code,
Date=CASE when Date = 20031102 then Date else null end,
Amount=CASE when Date = 20031102 then Amount else null end,
Date=CASE when Date = 20031103 then Date else null end,
Amount=CASE when Date = 20031103 then Amount else null end,
FROM tblSearch
ORDER BY code

[color=blue]
> --temp with each Code
> Drop Table #T0;
> Select Code
> Into #T0
> From tblSearch
> Order by Code;
>
> --temp with amounts for 1st date
> Drop Table #T1;
> Select Code, Date, Amount
> Into #T1
> From tblSearch
> Where Date = 20031102
> Order by Code, Date;
>
> -- amounts for 2nd date
> Drop Table #T2;
> Select Code, Date, Amount
> Into #T2
> From tblSearch
> Where Date = 20031103
> Order by Code, Date;
>
> --put everything together
> Select Distinct #T0.Code, #T1.Date, #T1.Amount 'd1', #T2.Date, #T2.Amount
> 'd2' from #T0
> Left Outer Join #T1
> On #T0.Code = #T1.Code
> Left Outer Join #T2
> On #T0.Code = #T2.Code
> Order By #T0.Code[/color]

[Chris]

Re: Joins on same table

The derived table approach gets me what I want -- one row per Code.

It seems that Coalesce doesn't help reduce the normal number of rows from
the Join.

Thanks very much for looking for a solution.

[Chris]

Re: Joins on same table .. solution with Temps

The derived tables gets both Amounts into the same row, while the Case
still results in two (Distinct) rows.

I need to get a better SQL reference -- the book I'm using does not cover
derived tables.

Thanks very much.

[louis nguyen]

Re: Joins on same table .. solution with Temps

"Chris" <chris@hicom.ne t> wrote in message news:<2bcNb.324 25$G04.6661104@ news4.srv.hcvln y.cv.net>...[color=blue]
> The derived tables gets both Amounts into the same row, while the Case
> still results in two (Distinct) rows.
>
> I need to get a better SQL reference -- the book I'm using does not cover
> derived tables.
>
> Thanks very much.[/color]

Use GROUP if you want combine them into the same row. DISTINCT only
filters the rows.

SELECT
Code,
Date=max(CASE when Date = 20031102 then Date else null end),
Amount=max(CASE when Date = 20031102 then Amount else null end),
Date=max(CASE when Date = 20031103 then Date else null end),
Amount=max(CASE when Date = 20031103 then Amount else null end)
FROM tblSearch
GROUP BY code
ORDER BY code

[Erland Sommarskog]

Re: Joins on same table

Chris (chris@hicom.ne t) writes:[color=blue]
> It seems that Coalesce doesn't help reduce the normal number of rows
> from the Join.[/color]

That's right. The coalesce() function takes a list of values as parameters,
and return the first value in the list that is not NULL. Since the second
query included a full join, any of a.code and b.code could be NULL, so be
sure that we had a value here, I used coalesce(a.Code , b.Code).



--
Erland Sommarskog, SQL Server MVP, sommar@algonet. se

Books Online for SQL Server SP3 at

http://www.microsoft.com/sql/techinfo/productdoc/2000/books.asp

[Chris]

Re: Joins on same table .. solution with Temps


Excellent!

-- Thanks

[Erland Sommarskog]

Re: Joins on same table .. solution with Temps

louis nguyen (louisducnguyen @hotmail.com) writes:[color=blue]
> SELECT
> Code,
> Date=max(CASE when Date = 20031102 then Date else null end),
> Amount=max(CASE when Date = 20031102 then Amount else null end),
> Date=max(CASE when Date = 20031103 then Date else null end),
> Amount=max(CASE when Date = 20031103 then Amount else null end)
> FROM tblSearch
> GROUP BY code
> ORDER BY code[/color]

Note that date literals requires quotes. 20031103 is a number, and
attempt to convert it to datetime results in overflow.


--
Erland Sommarskog, SQL Server MVP, sommar@algonet. se

Books Online for SQL Server SP3 at

http://www.microsoft.com/sql/techinfo/productdoc/2000/books.asp